The knowledge of the source of plasma cholesterol is relevant to the problem of human hypercholesterolemia. On regular diet the largest fraction of plasma cholesterol in man originates from synthesis. However, there are controversies about the mechanisms regulating cholesterol production, and whether synthesis occurs predominantly in the liver or in the intestinal wall. Intestinal cholesterol is carried exclusively by the lymphatic system. Patients with chyluria due to Filariasis are proposed as models to measure intestinal cholesterol synthesis after intravenous pulse labeling with radiocholesterol, circumventing inadequacies of a) the use of labeled precursors, and b) investigations in lower animals where cholesterol metabolism differs from man in many points. During metabolic balance on cholesterol free synthetic formula diets, intestinal lymphatic cholesterol, determined by gas-liquid chromatography, originates from three possible sources: a) local mucosal synthesis, b) absorption of the biliary component, c) blood plasma bathing the intestine. Sources a plus b are transported in chylomicrons, whereas fraction c is carried in other plasma and chyle lipoproteins. During the log linear phase of the isotopic decay curve of plasma radiocholesterol, the specific activity in urinary chyle chylomicrons, separated by ultracentrifugation, will be lower than in the other plasma and chyle lipoproteins if cholesterol delivered into the lymphatic system originates from local synthesis in addition to the sources b and c.